The present invention relates to the field of integrated circuits, and in particular to integrated circuits that include at least two circuit components that are formed on a common semiconductor substrate and which each have self-contained supply voltage systems.
Integrated circuits may include at least two circuit components that are formed on a common semiconductor substrate and which each have self-contained supply voltage systems. In addition, each of the two circuit components may include self-contained bonding spots for receiving an externally supplied voltage. Separate supply voltage systems of this type may be necessary to meet EMC requirements. In conventional technologies for highly integrated circuits, the semiconductor substrate is p-conductive and is connected to the power supply nodes of the two circuit components that carry the lowest voltage potential (e.g., “Vss”) among the applied potentials, such that the Vss potentials of the two circuit components are coupled by one substrate resistance.
One or more connections in the form of signal lines are often present between the two circuit components. The desirable isolation of the supply voltage systems for the individual circuit components may lead to problems in the event of excessive voltages, for example, electrical overstress (EOS). This is particularly true in the event of electrostatic discharge (ESD), since the separate supply voltage systems of the individual circuit components occupy a relatively smaller area and supply a smaller number of components than does a corresponding supply voltage system that services the entire integrated circuit. Therefore, such separate supply voltage systems react with relatively greater sensitivity to the switching operations of individual circuit components, and differential voltages are transferred from one circuit component to another through the signal lines and are thus able to reach sensitive circuit components, such as the gate-oxide layers, which may be destroyed by these voltages.
A prior art technique that attempts to solve this problem includes coupling the supply voltage systems for multiple circuit components integrated on a common semiconductor substrate using coupling circuits, as illustrated in FIG. 1. FIG. 1 is a schematic diagram illustration of a prior art integrated circuit 100 that includes first and second circuit components 1, 2, respectively. The first and second circuit components 1, 2 receive supply potentials Vcc1, Vss1, and Vcc2, Vss2, as illustrated, through associated bonding spots 5. Under normal operating conditions Vcc1=Vcc2 and Vss1=Vss2. The integrated circuit 100 also includes first and second coupling circuits 3, 4. The first coupling circuit 3 receives Vcc1 and Vcc2 on lines 102, 103 respectively, while the second coupling circuit 4 receives Vss1 and Vss2 on lines 104, 105 respectively. Each coupling circuit 3, 4 includes antiparallel connections of two PNP transistors 6. Whenever any excess voltage mutually disturbs the supply voltage systems of the first and second circuit components 1, 2, the transistors 6 produce a compensation of voltage, such that a portion of the current flows from the emitter to the base of each transistor 6, while the remainder of the current continues to flow to the collector of each of the transistors 6.
Each of the PNP transistors 6 has the semiconductor substrate as the collector, an n-doped well formed in the substrate as the base, and a p+ region inside the well as the emitter. The effect of this arrangement is that when one of the coupling circuits 3, 4 opens in response to an excessive voltage of one of the transistors 6, although part of the compensation current (from the emitter to the base) will flow from one supply voltage system into the other, another part of the compensation current nevertheless will unavoidably flow directly from the emitter into the substrate representing the collector.
Another problem with these conventional coupling circuits 3, 4 is the considerable area they utilize on the substrate. Such considerable area is required because each of the coupling circuits 3, (each one of which being required for the corresponding supply voltage to be compensated) has two transistors 6. An additional reason that considerable area is required is because essentially holes are involved in the current flow through the transistors 6. The mobility of holes is less than that of electrons, and therefore requires comparatively greater coverage areas of the doping zones to achieve a volume resistivity of the transistors that is sufficiently low for effective coupling.
What is needed is an integrated circuit that includes at least two circuit components and separate supply voltage systems therefore, where the integrated circuit has a coupling circuit with a relatively small surface area between the supply voltage systems.